Structural and photoluminescence properties of thin alumina films on silicon, fabricated by electrochemistry
Introduction
Anodic alumina films have received significant attention in recent years due to their interesting dielectric, optical and other properties, which make them very attractive for various applications. The possibility to grow porous alumina with regular vertical pores of controlled sizes on a silicon substrate opens important new perspectives for potential applications in electronic, optoelectronic and magnetic nanodevices. In this respect, it is very essential to fully understand the mechanism and the kinetics of growth of the films and the different parameters which influence their structure (anodising conditions, anodisation solution, etc.). However, while a lot of work has been devoted to the anodisation of bulk aluminium in order to get an alumina film on its surface (see Ref. [1] and references therein), very little work has been published on alumina films on a silicon substrate [2], [3], [4], [5], [6], [7]. Different methods of film growth were in general used in the above references, as for example reactive rf sputtering [4], low pressure metal–organic chemical vapor deposition [5], [6], electron beam evaporation [7] or electrochemistry [2], [3].
In this paper we investigate the growth of thin alumina films (thickness below 0.5 μm) on a silicon substrate by using anodisation in different acid aqueous solutions. The structure and properties of the obtained alumina films were found to depend on the electrochemical solution used and the thickness and composition of the initial film. The obtained films were measured for their photoluminescence (PL) properties, which also depended on film thickness and the anodisation conditions. The obtained results will be discussed below.
Section snippets
Sample preparation
Al thin films were deposited on p-type (100) Si wafers using electron gun evaporation from a target composed either of pure Al or an alloy of Al(1% Si) [8]. Prior to Al deposition, the Si wafers were cleaned in an H2O2:H2SO4 solution and an ohmic contact was formed on their backside. Al films of five different thicknesses, in the range of 15–500 nm, were deposited and the samples were then anodised in different solutions at room temperature. Anodisation was carried out under constant dc voltage
Conclusion
Aluminium thin films, either pure or containing 1% silicon, were deposited on a silicon substrate by electron gun evaporation and they were then anodised in different acid aqueous solutions (citric, oxalic or sulfuric) in order to obtain alumina thin films. The structure of the final film depended strongly on the initial aluminium film composition (pure Al or Al(1% Si)) and thickness, as well as on the anodisation solution. Anodisation of aluminium films of thickness higher than 0.5 μm in
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